In many electronic appliances and devices (e.g. electronic clocks, radios, CD players, computers, video games, etc.), the bulkiest part of the system is the power supply which, traditionally, requires a heavy isolation transformer and, sometimes, a heat sink and a cooling fan. The power supply is needed to convert the AC voltage from the wall outlet to a DC voltage that can be used by the system. For some systems that do not have a built-in power supply (e.g. portable computers), an external AC-to-DC adapter is needed to operate the systems from a wall outlet.
The reason for providing AC voltages to typical power outlets, such as a wall outlet, is that the only cost-effective way to convert an AC voltage to a DC voltage was to use a linear power supply. FIG. 1 shows the basic block diagram of a linear power supply 20. The isolation transformer 22 serves two purposes: 1) isolate the output from the input in order to meet federal safety regulations and 2) reduce the input voltage from a higher voltage (e.g. 110V) to a lower voltage (e.g. 5V). The reduced AC voltage is then rectified and filtered at 24 into a DC voltage. The series-pass element 26 regulates the output DC voltage by monitoring the loading at the output 28 by feedback and control 29. The drawback of the linear power supply is that, due to the low AC input frequency (60 Hz), both the isolation transformer and the filter capacitors have to be relatively large. Furthermore, the power conversion efficiency of a linear power supply is only about 40 to 50%. It is also impractical to attempt to fit a linear power supply into the size of an AC wall outlet. Thus, due to the large size requirements, conversion from AC-to-DC voltages is typically done inside or within the device that requires a DC supply voltage.
The progress of the power semiconductor technology in recent years has made a new type of power supply economically feasible. FIG. 2 shows a block diagram of a so-called "switch mode power supply" (SMPS) or "class D" power supply 30. In an SMPS, the AC input 32 is rectified and filtered at 34 into a DC voltage without going through an isolation transformer. A switching element 36 (usually a power transistor or transistors) will chop the DC voltage into a very high frequency AC voltage (up to several hundred KHz). This high frequency AC voltage is then fed to an isolation transformer 38 before being rectified and filtered again at 40 to provide the output 42 of the power supply. Since the transformer and the output filter only have to deal with a very high frequency AC voltage, the size of the transformer and the filter capacitors can be relatively small. In addition, since the switch element usually dissipates very little power, the efficiency of an SMPS is usually about 70 to 80%.
However, the advent of SMPS has only resulted in reducing the size, weight, and cost of power supplies inside or within the device that requires a DC supply voltage.
It is an object of the present invention to provide an improved power supply distribution technique and system.
It is a further object of the present invention to provide an improved AC-to-DC power supply conversion.
It is yet another object of the present invention to provide an improved method for powering devices which require DC supply voltages.
It is yet a further object of the present invention to provide DC voltages within an electrical outlet.
It is still another object of the present invention to provide an integrated circuit device for converting AC-to-DC voltages.
It is another object of the present invention to convert AC-to-DC voltages by a device attached to the normally inaccessible side of a wall outlet.